Question re single instance RAC node

I'm new to this list and am hoping there are some folks with RAC
experience. We running 10gR2 and are going to be implementing ASO in
order to use TDA to encrypt sensitive data. We have a second database
which also contains data which must be encrypted and in an attempt to
save licensing costs would like to put it on one of the nodes in the RAC
cluster. This raises a number of questions in my mind which I'm hoping
someone can shed some light on.

First, does the single instance database have to be a RAC database? I
have heard people making reference to a single node RAC instance and
must admit it doesn't make complete sense to me.

Secondly, if we are using ASM for the RAC instances is there any problem
with putting the database files for the non-RAC database on a file
system?

Finally, does anyone have any thoughts on the pros and cons of setting
up oracle like this. A single instance database on one node of a RAC
cluster.